Meh, I'm kind-of underwhelmed. The Sigma 70/2.8 Macro got here yesterday and I spent the morning playing with it. It isn't as sharp as I'd been led to expect, or maybe my lens is a dud. Either way, I don't think macro photography is right for me, or this isn't the right season for it, or Texas isn't the right place. I hate using tripods and the paper-thin DoF makes tripods a necessity. So, the close-focusing capability of what is probably a very nice macro lens is wasted on me.
As a portrait lens, the Sigma becomes redundent for me. Though the f/2.8 aperture should mean accurate auto-focusing, mine seemed to hunt quite a bit, and sixteen AF-screw turns from 1:1 to infinity takes a good while. The beercan focuses much faster and maybe a bit more accurately, too. F/2.8 is nice, but again, the lens isn't at its best there. Above f/4.5 the lens starts to act like a beercan with a bokeh upgrade; smoother and more circular OOF highlights. My beercan already behaves very well at 70mm, with plenty of sharpness and no CA to speak of, so I can't see carrying both lenses.
The Sigma 70mm is going back. I'm sure it's a good macro lens, but I learned my lesson about using a macro for portraiture. A side effect of this experience: I REALLY appreciate all the lenses I already own. I'll rent another body for my upcoming wedding and use the Tamron 17-50 on one and the beercan on the other. As for a lens purchase with my "allowance," I'll wait and see about the new Sigma 85/1.4, or maybe the Tokina 11-16/2.8.